The present invention relates to a method for fabricating a semiconductor device, and more particularly, it relates to a method for forming a conducting film serving as a lower electrode or an upper electrode of a semiconductor device including a capacitor dielectric film made from a perovskite type high dielectric constant or ferroelectric material.
A conducting film serving as a lower electrode or an upper electrode of a semiconductor device including a capacitor dielectric film made from a perovskite type high dielectric constant or ferroelectric material is made from a noble metal film having an oxidation-resistant property such as a platinum film, and the noble metal film is formed by sputtering.
In accordance with improvement in the refinement and the degree of integration of semiconductor integrated circuits, a DRAM cell included in a semiconductor integrated circuit is desired to be finer, and a capacitor device included in a DRAM cell is formed three-dimensionally. Thus, a concaved capacitor device has been proposed.
A method for fabricating a conventional semiconductor device including a concaved capacitor device will now be described with reference to FIG. 7A.
First, after forming an insulating film 2 of a silicon oxide film having a recess on a semiconductor substrate 1, a lower electrode 3 of a first platinum film is formed by sputtering on the walls and the bottom of the recess of the insulating film 2.
Next, after forming a capacitor dielectric film 4 of a perovskite type high dielectric constant material such as a BST (barium strontium titanium oxide) film on the lower electrode 3, an upper electrode 5 of a second platinum film is formed by the sputtering on the capacitor dielectric film 4.
Since a capacitor device is desired to be finer in accordance with demands for further refinement of a DRAM cell, the average plane size of the recess of the insulating film 2 where the lower electrode 3 is formed has been reduced to, for example, a shorter side of approximately 0.15 xcexcm and a longer side of approximately 0.3 xcexcm.
Since the aspect ratio of the recess of the insulating film 2 in this size is higher than a conventional one, the coverage is so low that the thicknesses of the lower electrode 3 and the upper electrode 5, namely, the platinum films formed by the sputtering, are reduced at the bottom corners, and in addition, an overhang is formed at the upper portion of the upper electrode 5.
When the thickness of the lower electrode 3 is small at the bottom corners, the platinum film used for forming the lower electrode is agglomerated, namely, platinum included in a portion with a small thickness moves to a portion with a large thickness, during annealing for forming the capacitor dielectric film 4 by CVD (chemical vapor deposition). As a result, the lower electrode 3 is disadvantageously disconnected at the bottom corners as shown in FIG. 7B.
When the thickness of the upper electrode 5 is small at the bottom corners, the platinum film used for forming the upper electrode 5 is agglomerated during annealing for improving the quality of the capacitor dielectric film 4. As a result, the upper electrode 5 is disadvantageously disconnected at the bottom corners as shown in FIG. 7B. Also, when an overhang is formed at the upper portion of the upper electrode 5, an empty space is disadvantageously formed in the upper electrode 5.
Accordingly, as disclosed in, for example, U.S. Pat. Nos. 6,162,712, 5,783,719, 5,929,267 and Japanese Laid-Open Patent Publication No. 11-292889, the platinum films used as the lower electrode 3 and the upper electrode 5 are formed by the CVD for attaining good coverage.
When the CVD is employed for forming the platinum film serving as the lower electrode 3, however, the platinum film is formed by the CVD on the insulating film 2 of a silicon oxide film, which degrades the morphology of the platinum film, namely, which results in forming micro irregularities on the surface of the platinum film. This leads to a problem of degradation in the quality of the capacitor dielectric film 4 formed on the platinum film.
Also, when the platinum film serving as the upper electrode 5 is formed by the CVD, the CVD is carried out on the capacitor dielectric film 4 of a BST film. Therefore, an organic substance such as carbon generated from the BST film and a material gas is caught in the platinum film, resulting in degrading the electric characteristic on the interface between the capacitor dielectric film 4 and the upper electrode 5.
In consideration of the aforementioned conventional problems, a first object of the invention is preventing a conducting film that is formed on the walls and the bottom of a recess of an insulating film to be used as a lower electrode from being disconnected at bottom corners as well as improving the quality of a capacitor dielectric film formed on the conducting film, and a second object is preventing a conducting film that is formed in a small recess to be used as an upper electrode from being disconnected at bottom corners and from having an overhang at an upper portion thereof as well as improving the electric characteristic on the interface between the capacitor dielectric film and the upper electrode.
In order to achieve the first object, the first method of this invention for fabricating a semiconductor device including a concaved capacitor device having a lower electrode, a capacitor dielectric film of a perovskite type high dielectric constant or ferroelectric material formed on the lower electrode and an upper electrode formed on the capacitor dielectric film, comprises a step of forming a conducting film to be formed into the lower electrode including sub-steps of depositing a lower conducting film by sputtering on walls and a bottom of a recess formed in an insulating film on a substrate; and depositing an upper conducting film on the lower conducting film by CVD.
In the first method for fabricating a semiconductor device, since the lower conducting film included in the conducting film to be formed into the lower electrode is formed by the sputtering, the conducting film to be formed into the lower electrode is improved in its morphology, which improves the quality of the capacitor dielectric film formed on the conducting film. Also, since the upper conducting film disposed on the lower conducting film is formed by the CVD, the conducting film to be formed into the lower electrode attains a uniform thickness. Therefore, although the lower electrode is formed in a small recess, the conducting film to be formed into the lower electrode is minimally agglomerated during annealing for forming a perovskite type high dielectric constant or ferroelectric material film to be used as the capacitor dielectric film. As a result, the lower electrode can be prevented from being disconnected at bottom corners.
In the first method for fabricating a semiconductor device, the lower conducting film preferably has a thickness of 0.5 nm through 5 nm.
Thus, the thickness of the lower conducting film can be made uniform, and hence, the upper conducting film can be stably formed on the lower conducting film by the CVD. Therefore, not only the conducting film to be formed into the lower electrode can attain a uniform thickness but also the lower electrode can be definitely prevented from being disconnected at bottom corners.
In order to achieve the second object, the second method of this invention for fabricating a semiconductor device including a capacitor device having a lower electrode, a capacitor dielectric film of a perovskite type high dielectric constant or ferroelectric material formed on the lower electrode and an upper electrode formed on the capacitor dielectric film, comprises a step of forming a conducting film to be formed into the upper electrode including sub-steps of depositing a lower conducting film by sputtering; and depositing an upper conducting film on the lower conducting film by CVD.
In the second method for fabricating a semiconductor device, since the lower conducting film included in the conducting film to be formed into the upper electrode is formed by the sputtering, an organic substance such as carbon generated from the perovskite type high dielectric constant or ferroelectric film and a material gas can be prevented from being caught in the lower conducting film. Therefore, the degradation in the electric characteristic on the interface between the capacitor dielectric film and the upper electrode can be avoided. Also, since the upper conducting film disposed on the lower conducting film is formed by the CVD, the conducting film to be formed into the upper electrode can attain a uniform thickness. Therefore, the conducting film to be formed into the upper electrode is minimally agglomerated during annealing for improving the electric characteristic of the perovskite type high dielectric constant or ferroelectric film, and hence, the upper electrode can be prevented from being disconnected at bottom corners. Furthermore, the conducting film to be formed into the upper electrode can be prevented from having an overhang.
In the second method for fabricating a semiconductor device, the capacitor device may be a concaved capacitor device or a stacked capacitor device.
In the second method for fabricating a semiconductor device, the CVD is preferably carried out in an oxidizing atmosphere.
Thus, the degradation of the perovskite type high dielectric constant or ferroelectric film used as the capacitor dielectric film can be avoided, and the self-catalytic effect can be suppressed so as to form the upper conducting film in a uniform thickness.
In the second method for fabricating a semiconductor device, the lower conducting film preferably has a thickness of 0.5 nm through 5 nm.
Thus, the lower conducting film can attain a uniform thickness, and hence, the upper conducting film can be stably formed on the lower conducting film by the CVD. Therefore, not only the conducting film to be formed into the upper electrode can attain a uniform thickness but also the disconnection of the upper electrode at the bottom corners and the formation of an overhang at the upper portion of the upper electrode can be definitely avoided.